package com.rogue.generator.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class IdGenerator {

    private final static Logger logger = LoggerFactory.getLogger(IdGenerator.class);

    private final long workerId;
    private final static long twepoch = 1288834974657L;
    private long sequence = 0L;
    private final static long workerIdBits = 4L;
    public final static long maxWorkerId = -1L ^ -1L << workerIdBits;
    private final static long sequenceBits = 10L;
    private final static long workerIdShift = sequenceBits;
    private final static long timestampLeftShift = sequenceBits + workerIdBits;
    public final static long sequenceMask = -1L ^ -1L << sequenceBits;
    private long lastTimestamp = -1L;

    public IdGenerator(final long workerId) {
        super();
        if (workerId > this.maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(
                    String.format("Worker Id can't be greater than %d or less than 0",
                            this.maxWorkerId));
        }
        this.workerId = workerId;
    }

    public synchronized long nextId() throws Exception {
        long timestamp = this.timeGen();
        if (this.lastTimestamp == timestamp) {
            this.sequence = (this.sequence + 1) & this.sequenceMask;
            if (this.sequence == 0) {
                timestamp = this.tilNextMillis(this.lastTimestamp);
            }
        } else {
            this.sequence = 0;
        }
        if (timestamp < this.lastTimestamp) {
            throw new Exception(
                    String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
                            this.lastTimestamp - timestamp));
        }

        this.lastTimestamp = timestamp;
        long nextId = ((timestamp - twepoch << timestampLeftShift)) | (this.workerId << this.workerIdShift)
                | (this.sequence);
        return nextId;
    }

    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) throws Exception{
        IdGenerator idGenerator = new IdGenerator(1);
        for(int i = 0;i < 100;i++) {
            logger.info(String.valueOf(idGenerator.nextId()));
        }
    }
}
